The invention relates to a device including a nozzle as a control device for setting a prescribed fluid mass flow.
It is known that such control devices consist in the simplest case of a so-called naval nozzle, which expediently consists, in an axially symmetric fashion, of a convexly converging nozzle-shaped part and an adjoining concave expansion. Such naval nozzles deliver a constant gas mass flow as long as the ratio of the pressure in the narrowest part of the nozzle to the pressure upstream of the naval nozzle seen in the flow direction does not exceed the value of 0.53 (in the case of diatomic gases). It is possible by means of the pressure gained in the expanded part of the nozzle to keep the quantity of air constant given a constant inlet pressure if the ratio of the pressure prevailing at the end of the expansion to the inlet pressure of the naval nozzle does not exceed a value of 0.85 to 0.9, in round figures.
Such known naval nozzles have the disadvantage that the gas mass flow blowing through them can be varied only via the inlet pressure of the nozzle. Given a wide range of the gas quantity to be varied, it is frequently necessary for a plurality of naval nozzles, which deliver, optionally or in combination with one another, the necessary gas mass flow, to be connected in parallel.